Identification and characterization of early and late antigenic proteins of Herpesvirus saimiri: Herpesvirus saimiri antigenic proteins labeled with 35S-methionine were immunoprecipitated from extracts of infected cells with specific antisera. Antigenic proteins were identified by fluorography following SDS polyacrylamide gel electrophoresis. Herpesvirus saimiri strain variability: We have recently completed our analyses of 20 new isolates of Herpesvirus saimiri using the restriction endonuclease digestion procedure. The 20 new isolates included 10 from wild caught Columbian squirrel monkeys, seven from wild caught Peruvian Squirrel monkeys and three from squirrel monkeys born to Peruvian parents at New England Regional Primate Research Center. Seventeen of the 20 isolates were distinguishable but three of the Peruvian isolates appeared to be identical. The three identical isolates were obtained from one colony born animal and two wild caught Peruvian monkeys. It is possible that these isolates were related epidemiologically.